At the end of April 2009, the U.S. Government Accountability Office released a report expressing concern about the Air Force’s modernization and maintenance of the GPS system. Constant replacement and upgrading of satellites is necessary, especially with hardware that’s been operating in space for almost two decades.

The GAO has calculated – using reliability curves for each operational satellite – that the probability of keeping a 24-satellite constellation in orbit drops below 95 percent in 2010, and could drop as low as 80 percent in 2011 and 2012. And if the Air Force doesn’t meet its goals for the next-generation GPS III satellites, the probability drops to around 10 percent in 2017.